The present invention relates to use of a storm water system for heat exchange and more particularly to a method and system for using an underground storm water system for heat exchange for building heating, ventilation, and air conditioning (HVAC).
Many buildings and other structures for which heating or cooling is needed provide temperature control using a closed loop system having a heat exchanger. A heat exchanger requires for operation a source for adding or removing heat from the structure. A common source for adding or removing heat that is known in the art involves capture of geothermal energy, which is the energy from the earth or temperature from the earth, using a heat exchanger.
The operation of a heat exchanger can be understood by reference to the radiator of a car, which is one form of heat exchanger. In a car, heat from the engine is transferred to coolant circulated within the engine. The coolant is then pumped into a radiator, where heat is transferred to the surrounding air, and the cooled coolant is returned to the engine to begin the cycle again. In this manner, heat is transferred from the engine so as to maintain the temperature of the engine below the boiling point.
A similar approach is used to cool a structure, such as a building. A heat exchanger connected to a building takes advantage of the temperature difference between the ambient or surface air temperature and a constant temperature source, such as relatively constant subsurface temperature (subsurface temperature, as used herein, refers to the temperature at a depth of several feet below the surface of the earth, the depth of which depends on the climate and other conditions of the area; below this set depth, the temperature is known to generally remain constant). The heat exchanger is used to transfer the temperature difference from the subsurface area to the building located on the surface. Because the subsurface temperature is typically above the surface temperature in winter, heat may be transferred to the structure via the heat exchanger to heat the structure, and because the subsurface temperature is typically less than the surface temperature during the summer, the heat exchanger can transfer the heat in the building from the surface to the subsurface to cool the structure.
The relatively constant subsurface temperature of the earth is commonly considered when laying water pipes or sewer pipes, as well as when building a structure. In these cases, it is often important that the pipes or structure be located below the frost linexe2x80x94the area within the ground below which water freezes. Ground below the frost line has a typically somewhat higher temperature than the ambient air temperature at the surface in winter, and typically somewhat lower temperature than the ambient air temperature at the surface in summer.
It is known in the art to provide this heat exchange by digging an excavation, referred to as a field, for the structure, planting a closed loop heat exchanger in the earth for capturing or releasing heat. A problem with this approach is that the heat transfer coefficient between the coolant contained in the closed loop of the heat exchanger and the solid of the soil in which the loop is located is substantially less than the heat transfer coefficient for liquid-to-liquid or liquid to gas heat transfer. As a result, heat transfer using soil results in inefficiency compared to heat transfer using a liquid or gas.
For a completely unrelated reason to heat transfer, it is also known in the art to provide subsurface storage of storm water for businesses and other developments, such as parking lots. These systems are referred to as underground storm water chamber systems. Subsurface storage can include storage tanks specially designed and constructed for these facilities, and storm water is also storable in above-ground constructs, such as surface ponds or impoundments.
Underground storm water chamber systems can be either detention systems, retention systems, or first flush attenuation systems. Detention systems store a calculated volume of storm water in the chamber. Water is released at a predetermined rate to an outflow structure. Retention systems also store a calculated volume of storm water in the chamber; however, the primary drainage mechanism in retention systems is infiltration into the soil. First flush attenuation systems are similar to retention systems; however, they have limited capacity. Once capacity has been met, excess storm water is released into an outlet. First flush attenuation systems are often used to take advantage of the soil""s filtration and renovation capabilities when the inital runoff contains a high percentage of pollutants. The present invention can be used in conjunction with any form of underground storm water chamber system.
A storm water management system is designed for managing the discharge of water from new construction so that the volume of water that leaves the site is no greater that the volume before the construction began. For example, if the site was a meadow with trees and grass, typical runoff levels would be relatively small, such as ten percent of the rainfall, with ninety per cent of the rainfall being absorbed into the ground. After construction on such a site, however, runoff may be much greater than it was when the site was a meadow.
Whenever new construction occurs or there are other improvement to property, in general, a calculation must be made to ensure that sufficient runoff storage capacity for the geographical area is provided, such that the base line of rainfall that is anticipated in the area from historical data is maintained. The calculations for storage capacity are predicated on the historical rainfall information, so that the storage capacity of the storm water management system will have the capacity to contain the predicted amount of runoff that can be expected with the new construction or other improvement, and this capacity maintained and metered out at the same rate of discharge that was occurring before the construction.
This discharge from the storm water system typically is made to a storm drain, which most municipalities and incorporated townships have installed to keep water or storm water from collecting on the surface. In more rural areas, this discharge may typically occur onto neighboring property or into open swales or ditches along roadways. Municipal systems that combine both sanitary and storm water systems typically further include backflow preventors installed from the storm water management system, such that no sanitary effluent can back up into the system.
In order to accomplish the runoff collection and discharge needed, a typical storm water collection system collects runoff as quickly as possible. For example, the system might include a thirty-six-inch pipe leading into the storm water management collection area to allow for significant inflow of runoff. The same system might also have only a four-inch diameter exit pipe to control the discharge. As a result, during a rainfall event, the system typically becomes inundated with runoff, which is then discharged at a lower flow rate through the exit pipe. Thus, the net effect of collected rainfall on the property during a rainfall event is that downstream receivers of the discharge receive the same amount of water, which is metered out over time, as was received prior to the new construction or other improvement.
Typical storm water management systems are further designed such that no runoff or only a small amount of runoff normally remains in the system. In these systems, the small amount of runoff typically remains in the system solely for water quality management purposes. These water quality management purposes, which are also unrelated to heat exchange, are generally mandated by the local water quality control authority, requiring that the quality of the water discharged from the storm water management system be of the same quality as the rain water.
It is also known in the art to provide underground storage using prefabricated units that are interlockable. An example of such prefabricated units is the Maximizer Chamber System made by Infiltrator Systems Inc. of Old Saybrook, Conn. In this system, rows of individually prefabricated chambers are interlocked to form a continuous storage space that is structurally tested to withstand high surface pressures, as from vehicles parked above the system.
Because underground storm water chamber systems are typically located below the frost line, any water within these systems will reach an equilibrium temperature regardless of the seasonal air temperature at the surface above the system. For the same reasons as described above, this equilibrium temperature is typically below the surface air temperature during summer and above the surface air temperature during winter.
There is a need for a method and system for utilizing the intrinsic heat properties of water stored in a storm water chamber system for operation in conjunction with conventional HVAC systems of structures, such as buildings or other facilities, located near the storm water chamber system to provide efficient heating and cooling of these structures. There is a further need to utilize a liquid-to-liquid or liquid-to-gas heat exchange for heating and cooling such facilities in conjunction with use of a storm water chamber system.
It is an advantage of the present invention to solve the problems of the prior art by utilizing existing excavation made for other purposes to provide a location for a heat exchanger for a structure.
It is a further advantage of the present invention to provide a method and system for utilizing the energy of water stored in a storm water chamber system for operation with conventional HVAC systems of buildings or other facilities located near the storm water chamber system to heat and cool these facilities.
It is a further advantage of the present invention to provide for a heat exchange system locatable within prefabricated storm water chamber chambers. It is a further advantage of the present invention to provide for an interlockable heat exchange system that is interlockable with units of a storm water chamber system.
It is a further advantage of the present invention to provide for a method and system for retaining a minimum volume of water within a storm water chamber system having a heat exchange element, such that the heat exchange element remains immersed within retained runoff in the system.
It is a further advantage of the present invention to provide for a method and system for feeding back information from the storm water chamber system to the heat exchange portion of an HVAC system of a building or other facility to increase the efficiency of the system.
An embodiment of the present invention utilizes the excavation for a storm water management system to provide a source for capture of geothermal energy. This embodiment thereby uses a liquid-to-liquid or liquid-to-gas transfer ratio because the coil containing the liquid or gas medium of the heat exchanger is immersed in the liquid runoff that is contained within the storm water management system.
An embodiment of the present invention includes a closed loop heat exchanger system having connections by, for example, pipes containing a fluid or gas heat exchanger medium, and other components. The components of this embodiment include a pair of heat exchanger portions connected by a loop, and a pump that serves as a circulator for the heat exchange medium. In an embodiment of the present invention, the circulator moves the medium between an above ground heat exchanger, such as a radiator, for example, located in a building, and a below ground heat exchanger that includes coils located within a storm water chamber system. An embodiment of the present invention further includes a sensing device, such as a thermocouple, and feedback loop for HVAC control, to improve efficiency at ambient temperatures near the subsurface temperature.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become more apparent to those skilled in the art upon examination of the following or upon learning by practice of the invention.